Structural element having a high stress discontinuity and a fiber reinforcement mat embedded therein

ABSTRACT

A fiber reinforcing mat is used proximate a through hole in an automotive structural element in order to reinforce the element in the area approximate the through hole. The fiber reinforcing mat is comprised of a warp having a plurality of radially extending loops and a weft which is woven through the loops in a spiral fashion. Since the weft is configured as a spiral, weft material is more dense in the area close to the through hole than in the area distal of the through hole. Consequently, the stiffness of the structural element decreases gradually in radial directions away from the through hole.

FIELD OF THE INVENTION

The present invention relates to a fiber reinforcement mat for compositestructures. More particularly, the present invention relates to fiberreinforcement mats for composite structures wherein the reinforcementmats are utilized around discontinuities, such as through holes, in thestructures.

BACKGROUND OF THE INVENTION

In the automotive industry, vehicles are configured of structuralelements such as struts, beams and panels. Traditionally, thesestructural elements have been made of metal, but lately use has beenmade of resin-type materials which are frequently reinforced with fiberdepending on the use to which the structural element is put. Structuralelements are joined to one another by bolts, rivets or screws which passthrough holes in the structural elements. Areas of the structuralelements proximate the holes are subject to stress and fatigue whichover time can cause cracks and perhaps eventual failure of thestructural element.

In order to remain competitive in the automotive industry, it is veryimportant to keep costs as low as possible. This can be accomplished byreducing the amount of material for making a particular component, suchas a panel, and by simplifying the fabrication process. It is possibleto produce thinner panels which use less material and perhaps lessreinforcement by only reinforcing the panels where necessary. Forexample, if panels are only reinforced proximate through holes, or evenonly heavily reinforced proximate through holes, then the overallthickness of a panel can be reduced so as to use less material.

In addition to reducing costs less material reduces the weight of acomponent, such as a panel. Weight reduction has the advantage ofreducing fuel consumption and the amount of material which must bedisposed of or recycled once the vehicle is no longer in service.

In the automotive industry, very slight savings and expense and weightcan become very important when one considers that there are tens ofmillions of vehicles manufactured and in service. Accordingly,incremental improvements which may appear to be relatively modest assumeenormous importance when combined with numerous other incrementalimprovements which reduce costs and vehicle weight.

SUMMARY OF THE INVENTION

It is a feature of the present invention to provide a new and improvedstructure for reinforcing discontinuities in structural elements such ascomposite panels, struts, blocks, beams and the like.

The present invention is directed to a fiber mat for reinforcing astructural member proximate a location of high stress in the structuralmember. The fiber mat has a central opening therethrough with warpmaterial projecting radially from the central opening. Weft material iswoven through the warp material at a higher concentration proximate thecentral opening than distant from the central opening to provide agradual reduction in density of weft material in the radial directionaway from the central opening.

In another aspect, the present invention is directed to a combination ofa structural member having fiber reinforcement, the fiber reinforcementbeing configured as a mat having warp material extending radially fromthe discontinuity. Weft material is woven through the warp material, theweft material being more densely concentrated proximate thediscontinuity than distally of the discontinuity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view partially in cross-section showing a panel orother structural element reinforced with a fiber mat, the panel beingriveted to another structural element;

FIG. 2 is a top view of a fiber reinforcing structure utilized within astructural element of FIG. 1; and

FIG. 3 is an elevational view taken along lines 3--3 of FIG. 2.

DETAILED DESCRIPTION

Referring now to FIG. 1, there is shown an assembly comprising a firststructural element 10, which is configured in accordance with theprinciples of the present invention and a second structural element 12to which the first structural element 10 is secured by a rivet, or otherfastening member 14, extending through a through hole 16 in the firststructural element and a through hole 18 in the second structuralelement. The structural element 10 may for example be a composite panelwhich may be made of a resin material which is either generallyreinforced or not reinforced depending on the use to which the panel isput. For the purposes of this discussion, the structural element 10 isconfigured as a composite panel 10 having a first surface 18 and asecond surface 19 with a first fiber reinforcement mat 20 proximate thefirst surface 18 and a second fiber reinforcement mat 22 proximate thesecond surface 19. The component panel 10 is preferably molded, extrudedor otherwise configured of a resin-type material 23.

Referring now to FIG. 2, there is shown one of the fiber reinforcingmats 20 or 22, both of which mats have substantially the same generalconfiguration. The reinforcing mat 20 or 22 has a central opening 24through which a rivet, bolt or other fastening means extends when themat is incorporated into a composite structure such as the panel 10 ofFIG. 1.

Extending radially from the central opening 24 are a series of spacedradially disposed loops 26 which extend 360° around the opening 24. Theloops 26 may be formed of a single strand of reinforcing fiber 28 or maybe configured of separate strands arranged in loops. A preferablearrangement is to have a single strand. This single strand of fiberforms a warp of the woven fiber mat 20 or 22. The single strand 28 ormultiple strands forming the loops 28 may be either a monofilament or apolyfilament strand.

Woven through the warp formed by the loops 26 is a weft 30. The weft 30is a single monofilament or polyfilament strand of material which, as isseen in FIG. 3, goes over one leg, a loop 26 and beneath the next leg ofthe loop second length in alternating fashion around the entire array ofloops. As is also evident from FIG. 2 and FIG. 3, the weft 30 is wovenas a single strand woven as spiral which is tightly woven proximate thecenter hole 24 and progressively less tightly woven as the spiralprogresses toward the periphery 34 of the mat 20 or 22.

By having the spiral formed of the weft 30 more tightly woven near thecentral hole 24, more reinforcing material is utilized proximate thehole which makes the composite panel 10 into which the fiber reinforcingmat is inserted much stronger. This is because the hole 24 is coaxialwith the through hole 16 in the panel 10 where higher stress is appliedupon applying force to the panel. As the distance from the opening 24decreases, it is desirable to place the turns of the weft 30 further andfurther apart so that there is a gradual reduction in fiber densityallowing stress at the through hole 16 and the panel 10 and the hole 24to dissipate gradually in the panel out to the periphery 34 of the fibermat 20 or 22.

By having the above described spiral reinforcement arrangement, abruptdiscontinuities in the strength of the composite panel 10 are minimizedresulting in a panel which is less likely to experience cracks due toimpacts and fatigue. Stiffness of the panel 10 progressively decreasesin radial directions away from the hole 24 providing a structural memberwhich can be both strong and flexible. This structure, which facilitatesgradual dissipation of stress, also provides panels (or other structuralelements) which can be both lighter and less expensive to manufacture.

Referring particularly to the configuration of FIG. 3, it is seen thatfirst and second fiber reinforcing mats 20 and 22 are used, however, insome applications, only a single fiber mat may be used and in otherapplications more than two fiber mats may be used. In a number ofapplications, it is preferable to dispose the fiber mats 20 and 22 nearopposed surfaces 18 and 19 of the panel 10 because it is at the surfaceof panels that panels tend to initially crack due to fatigue and impact.After these cracks form, they propagate both radially from the source ofstress and axially from the source of stress in the direction of thethickness of the panel.

The warp fiber 28 and weft fiber 30 may be of the same material ordifferent materials. The materials may be high strength materials suchas carbon fiber material or may be, for example, glass fibers or perhapshigh strength resin fibers. The particular fiber chosen depends on theapplication to which the panel or structural member is put. The materialof which the panel 10 is made is in all likelihood resin material whichis configured to whatever shape the panel is to assume. The panel 10 maybe configured by resin-transfer molding, by injection-compressionprocesses or any other process. In the automotive industry, the panel 10exemplary of structural elements which are particularly useful ineliminating steel reinforcement pads and panels for high strengthapplications such as seat belt anchors, engine mounts and seatattachments.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention, and withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

What is claimed is:
 1. In a structural element having a high stressdiscontinuity therein, the improvement comprising:at least one fiberreinforcement mat embedded in the structural element and surrounding thediscontinuity, the mat having warp material radially extending outwardlyfrom the discontinuity and weft material woven through the warpmaterial, the weft material being circumferentially positioned, moredensely concentrated, and radially closer together proximate thediscontinuity than distal of the discontinuity.
 2. The improvement ofclaim 1, wherein the weft material is configured as a spiral woventhrough the warp material, the turns of the spiral being radially closertogether proximate the discontinuity than distal of the discontinuity.3. The improvement of claim 2, wherein the warp material is configuredfrom a single strand which forms a series of loops with each loopextending radially of the discontinuity.
 4. The improvement of claim 3,wherein the discontinuity is a through hole through the structuralelement.
 5. The improvement of claim 4, wherein the structural elementhas first and second opposed surfaces extending thereon proximate thehole and wherein one fiber reinforcement mat is disposed proximate thefirst surface and another fiber reinforcement mat is disposed proximatethe second surface.
 6. The improvement of claim 1, wherein thestructural element is primarily comprised of a resinous material andwherein the reinforcing fiber mat is embedded in the resinous material.7. The improvement of claim 5, wherein the structural element is securedto another structural element to form part of an assembly in anautomobile vehicle.
 8. The improvement of claim 1, wherein thestructural element is made of resinous material and has first and secondoppositely facing surfaces; wherein the discontinuity is a hole throughthe structural element, and wherein there are two fiber reinforcementmats, one embedded in the structural element adjacent each surface. 9.The improvement of claim 1, wherein the discontinuity is a hole throughthe structural element and wherein the element further includes afastener extending through the hole, the fastener engaging at least oneof the surfaces and applying compressive stress thereto.